Particulate matter filters are increasingly used in automotive emissions systems for reducing particulate concentrations in engine exhaust. However, over time, such filters can suffer irreversible decreases in trapping efficiencies as the filter develops cracks due to uncontrolled temperature excursion during the filter regeneration process, by means of which the soot accumulated in the filter is burned off under controlled engine operating conditions. Losses in trapping efficiency may result in increased particulate matter emissions well above the regulated limit.
Increasingly stringent particulate matter emissions standards and proposed government-mandated on-board diagnostic (OBD) requirements for monitoring the trapping efficiency of a particulate filter have stimulated much research into new techniques for monitoring particulate filter performance. Currently, only laboratory grade instruments are available for particulate matter measurements. Such instruments typically measure particulate concentrations via optical, gravimetric or electrical methods. These instruments typically require controlled operating conditions and extensive calibration for proper functioning. Furthermore, some of these instruments, such as instruments that utilize optical measurement techniques, may require periodic cleaning. Therefore, these instruments may be too expensive and difficult to use under normal automobile operating conditions to be a practical solution to monitoring particulate emissions in automobiles. Furthermore, performing a diagnostic on such sensors may be difficult in an on-board setting due at least in part to the above-described problems.
These and other problems with particulate sensor diagnostics may be effectively and efficiently addressed by an apparatus comprising an internal combustion engine; an exhaust system in communication with the engine, a particulate sensor associated with the exhaust system, and a controller in electrical communication with the particulate sensor, wherein the controller is configured to determine a change in a rate of exhaust flow in the exhaust system, to compare the change in the rate of exhaust flow to a preselected threshold rate of change; and if the change in the rate of exhaust flow has a preselected relationship to the preselected threshold rate of change, then to determine a degradation of the sensor. In some embodiments, the particulate sensor may comprise an image charge sensor.